Graphics Power Management not working under Sonoma?!

I am using RX 580 8GB - works fine under Windows 10 (a bit noisy) and Mojave (very quiet), but if I run a 3D game under Sonoma, the fans ramp up very rapidly to 100% and STAY THERE !!!. I need to reboot the computer to reset the GPU fans :-(

ie: even after quitting the offending game(s), the GPU fans stay at 100%, and BOY ARE THEY LOUD !!!

Has anyone else come across this behaviour?